1. Field of the Invention
The present invention relates to a medical diagnostic system and, more particularly, to a cable protection and identification system which ensures that each cable of a patient cable bundle is connected to an appropriate electrode and the electrodes are properly placed on predetermined locations of a patient.
2. Description of the Prior Art
It is common today to utilize medical diagnostic systems that have cables which attach to electrodes placed on a patient's body. For example, as shown in FIG. 1A, one type of ECG monitoring device 10 includes a cable bundle 11 having ten individual electrode cables 12, including four limb cables RL, RA, LA and LL and six chest cables, including C1, C2, C3, C4, C5 and C6. Each electrode cable 12 includes a clip (not shown) for connecting to a corresponding electrode 14 provided on a patient 13. Signals received by cables 12 are input via cable bundle 11 to monitoring device 10 and processed for output by audio/visual output 18. The output is used by a doctor, for example, to interpret the function of a patient's heart.
As used herein, the term patient refers to both humans and animals, although in a preferred embodiment patients are humans.
In its basic form, the typical ECG monitoring device 10 includes input processing circuitry 16 for providing functions including analog amplification and conditioning of the signals input via electrode cables 12. The conditioned signals are then input to lead signal processing circuitry 17 which performs functions including processing the signals input by electrode cables 12 and generating the twelve lead waveform signals. The lead waveform signals are then output to audio/visual output 18, which typically includes a display. For example, audio/visual output 18 can include a video monitor or a printer for printing out the lead waveform signals, and can include a tape drive, hard drive or other type of storage device for storing the signals. Input processing circuitry 16 typically monitors each individual electrode cable 12 signal continuously, for detecting pacemaker spikes, noise, 50/60 Hz power noise or loose cables not connected to the electrodes. This information can then also be output by audio/visual output 18 so that an operator can take appropriate action. Typically, in order to minimize the level of noise on the cables 12, each cable 12 is a shielded cable including a signal carrying core wire 20 surrounded by a grounded shield 19. Typically, each of the shields 19 is connected to ground in the ECG monitoring device 10.
Monitoring device 10 will now be explained in more detail below by reference to FIGS. 1B and 1C. Input processing circuitry 16 includes analog processing circuitry 16a, analog to digital converters 16b and digital processing units 16c. As shown, only nine sets of these components are typically necessary, since one limb lead input is typically provided to each analog processing circuit 16a as a common reference input. After processing by circuitry 16a and conversion by converters 16B, the digital signals are input to processing units 16c. Input processing circuitry 16 is capable of monitoring for a loose cable 12, for example, and outputting a signal when one is detected. For example, analog processing circuitry 16a and processing unit 16c can monitor the source impedance which is comprised of the impedance of the supply lines between the electrode 14 and the input processing circuitry 16 as well as the patients tissue impedance and electrode transfer impedance During interruptions, such as may occur when an electrode is removed from the patient, the impedance value will exceed a predetermined upper limit. Upon detecting this event, processing unit 16c will provide an output to controller 17a which in turn can provide an audio and/or visual signal via audio output 18a and signal display 18b.
The processed cable signals output from each of processing units 16c are input to digital lead processing circuitry 17b as shown in FIG. 1C. Digital lead processing circuitry 17b processes the cable signals in a known manner and outputs 12 lead waveform signals to signal display 18b for display to an operator.
Prevention of improperly placed cables and electrodes is important in order to achieve accurate measurements from the patient and to obtain a correct diagnosis. Further, protection of the patient and equipment from unwanted signals entering cables not connected to the patient is desired. One type of conventional cable identification system, as shown in FIG. 1A, is known as a 12 lead electrocardiogram (ECG) monitoring system. Although known as a 12 lead system, as described above, only 10 cables are necessary, with the system creating the 12 lead waveforms from those 10 cable inputs. This known system includes a 10-cable ECG cable bundle 11 in which each of the ECG cables 12 are marked with an electrode identifier label which indicates the respective electrode to which each of the ECG cables should be connected. For example, the 4 limb lead cables are marked RA, LA, RL, LL, respectively and the 6 chest lead cables are marked C1, C2, C3, C4, C5 and C6, respectively. As is well known in the art, each cable 12 is connected to a corresponding one of ten (10) electrodes 14 attached to the patient 13 at predetermined positions, as shown. In this manner, the cables 12 are typically marked to identify the electrode 14 on the patient 13 to which each cable 12 is to be connected. Similarly, for an 8-lead vector electrocardiogram (VCG) cable 21, as shown in FIG. 2, the leads 22 are marked RL, I, A, H, E, C, M and F. For another 8-lead VCG cable, not shown, the leads 22 are marked RL, RA, LA, LL, Neck, Chest, 45 degrees and Back.
Under non-stressful conditions, these conventional systems including marked cables have achieved a certain amount of success at reducing the number of improperly placed cables. However, under stressful conditions which may occur frequently in a medical environment, it may be difficult to quickly read or understand the text on the labels placed on the ECG cable. This can result in the ECG cable being connected to the wrong electrode.
Accordingly, there is a need for an identification system for preventing improperly placed cables on a patient. Such a system will assist in obtaining accurate measurements and correct diagnosis of patients.
Further, conventional systems are susceptible to unwanted signals entering cables not connected to the patient. That is, loose ECG cables may come in contact with nearby power sources such as other medical equipment and unwanted signals may damage the input electronics attached to the patient cable and stray DC or AC current may be distributed into the input electronics and even into the patient.